Question

The application icon, typically displayed in the upper left corner of the
application top-level windows, is set by calling the
QWidget::setIcon() method on top-level widgets.

In order to change the icon of the executable application file
itself, as it is presented on the desktop (i.e. prior to application
execution), it is necessary to employ another, platform-dependent
technique.

• Setting the Application Icon on Windows
• Setting the Application Icon on Mac OS X

Setting the Application Icon on Windows

First, create an ICO format bitmap file that contains the icon image. This
can be done with e.g. Microsoft Visual C++: Select "File|New...", then
select the "File" tab in the dialog that appears, and choose "Icon". (Note
that you do not need to load your application into Visual C++; here we are
only using its icon editor).

Store the ICO file in the source code directory of your application,
for example, with the name, "myappico.ico". Then, create a text file
called e.g. "myapp.rc" in which you put a single line of text:

IDI_ICON1               ICON    DISCARDABLE     "myappico.ico"

Lastly, assuming you are using qmake to generate your makefiles, add this
line to your "myapp.pro" file:

RC_FILE = myapp.rc

Regenerate your makefile and your application. The .exe file will now be
represented with your icon in e.g. Explorer.

If you do not use qmake, the necessary steps are: first, run the "rc"
program on the .rc file, then link your application with the resulting
.res file.

Setting the Application Icon on Mac OS X

The application icon, typically displayed in the application dock
area, is set by calling QWidget::setIcon() on a top-level widget. It
is possible that the program could appear in the application dock area
before the function call, in which case a default icon will appear
during the bouncing animation.

To ensure that the correct icon appears, both when the application is
being launched, and in the finder, it is necessary to employ a
platform-dependent technique.

Although many programs can create icon files (.icns), the recommended
approach is to use the Icon Composer program supplied by Apple (in the
Developer/Application folder). Icon Composer allows you to import several
different sized icons (for use in different contexts) as well as the masks
that go with them. Save the set of icons to a file in your project
directory.

If you are using qmake to generate
your make files, you only need to add a single line to your .pro
project file. For example, if the name of your icon file is
myapp.icns, and your project file is myapp.pro, add this line
to myapp.pro:

RC_FILE = myapp.icns

This will ensure that qmake puts your
icons in the proper place and creates a Info.plist entry for the
icon.

If you do not use qmake, you must do
the following manually:

1. Create an Info.plist file for your application (using the
   PropertyListEditor, found in Developer/Applications).

2. Associate your .icns record with the CFBundleIconFile record in the
   Info.plist file (again, using the PropertyListEditor).

3. Copy both the icns and your Info.plist into your application bundle
   Resource directory.